I have a Nikon D810 with the option of turning on exposure smoothing in the interval shooting area. I was just wondering if I should turn exposure smoothing off or have it turned on while doing interval shooting with the intention of using lrtimelapse afterwards.

the main problem with this option is, that it will work only with the internal intervalometer and you will have no control about what the camera is doing. You won't even see a preview on the display while shooting.
I recommend shooting transitions (day/night or night/day) with the holy grail approach, outline here on many places and in my Ebook. Best would be to use an external intervalometer to trigger the camera. This will give you the maximum control and deliver the best results. You can even automate everything with "Auto Holy Grail" in qDslrDashboard.
It's a bit more to learn, but once you've mastered it, you'll never want to go back.
Read this faq also: http://forum.lrtimelapse.com/Thread-why-...ority-mode

Thanks for the advice. I'll try out what you said.